Automotive vehicles with internal combustion engines are typically provided with both a starter motor and alternator. In recent years, a combined alternator and starter motor has been proposed. Such systems have a rotor mounted directly to the crankshaft of the engine and a stator sandwiched between the engine block and the bell housing of the transmission. During initial startup of the vehicle, the starter/alternator functions as a starter. While functioning as a starter, the starter/alternator rotates the crankshaft of the engine while the cylinders are fired.
After the engine is started, the starter/alternator is used as a generator to charge the electrical system of the vehicle.
Many vehicles have turbochargers incorporated with the engine. These turbochargers are commonly referred to as exhaust-gas turbochargers. A turbocharger consists of two machines: a turbine and a compressor mounted on a common shaft. The turbine is coupled to the exhaust system and uses the energy obtained in the flow of the exhaust system to drive the compressor. The compressor in turn, draws in outside air, compresses it and supplies it to the cylinders. The compressed air increases the power output of the engine.
Exhaust gas turbochargers operate using the mass flow of the exhaust gas. Thus, some time is associated with providing enough exhaust gas to rotate the turbocharger at a sufficient speed to provide compression at the output of the turbocharger. Such time is typically referred to as turbo lag. During turbo lag the engine output power is less than that when the turbocharger is operating.
In foreseeable automotive applications, the engine may be shut down during stops (e.g., red lights). When the accelerator is depressed, the starter/alternator starts the motor and the engine will resume firing. Thus, many startups may occur over the course of a trip.
It would therefore be desirable to reduce the amount of turbo lag and thus increase the amount of power of the engine during startup.